This pilot study is based on the effect of estrogen administration on male rats. The mode of action will be explored in young, mature and old rats, comparing the effect of denervation alone, estrogen alone and the association of estrogens and denervation. The normal group will result from a joint project utilizing the same parameters, that is to say in vitro contractility study and collagen determination of bladder strips. The determination of the density of cholinergic fibers will be done using a histochemical method. The following hypotheses will be tested: Estrogens act upon detrusor contractility through the parasympathetic nervous system. Estrogen will be less effective on detrusor contractility in aged rats and would represent a marker of aging. Denervation and aging are both responsible for the development of collagen deposits in the bladder wall responsible for an impairment of bladder contraction.